Power semiconductor module for an inverter circuit and method of manufacturing the same

ABSTRACT

A semiconductor device according to the present invention includes a semiconductor chip, a conductive member for supporting the semiconductor chip, a joint material provided between the conductive member and the semiconductor chip, and a release groove formed on the surface of the conductive member and arranged away from the semiconductor chip with the one end and the other end of the release groove connected to the peripheral edges of the conductive member, respectively.

TECHNICAL FIELD

The present invention relates to a semiconductor device, and moreparticularly to a power semiconductor module widely adopted for aninverter circuit and so forth and a method of manufacturing the powersemiconductor module.

BACKGROUND ART

For example, patent literatures 1 and 2 each disclose a semiconductordevice equipped with an island such as a die pad and a semiconductorchip disposed on the island. The semiconductor chip is bonded onto theisland using a molten solder.

PRIOR ART DOCUMENT Patent Literature

-   Patent literature 1: Japanese Unexamined Patent Application    Publication 2011-155286-   Patent literature 2: Japanese Unexamined Patent Application    Publication H6-37122

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Conventionally, a semiconductor chip was bonded onto an island bypressing and crushing a plate-shaped molten solder or a solder pastewith a semiconductor chip, causing the solder to be widely dispersed ina space formed between the semiconductor chip and the island. However,such conventional bondings often create problems such as solder leakageand solder shrinkage.

Solder leakage is a phenomenon in which a molten solder leaks outside asemiconductor chip. A leaked solder easily gets on the surface of asemiconductor chip to thus shorten a distance between the end of a rearsurface contact to a semiconductor chip and the surface of thesemiconductor chip, thereby rendering a withstand voltage of thesemiconductor chip lower than an original withstand voltage that dependson the thickness of a chip.

Meanwhile, solder shrinkage is a phenomenon in which a space (void)having no solder therein is created between a semiconductor chip and anisland. The void is finally filled with a resin with relatively lowthermal conductivity, otherwise remains as a vacant region, and thus theheat dissipation capability of the semiconductor chip can be decreased.Further, a portion of the semiconductor chip cannot be supported by asolder to thereby form a structure in which the portion extends outsidethe solder, so that stress concentration easily takes place at the baseof the structure. Consequently, cracks are liable to form during theprocess of a thermal cycle in which a rise and fall in temperature isrepeated.

Accordingly, there is a need for eliminating both the solder leakage andsolder shrinkage at low cost.

The object of the present invention is to provide, at low cost, asemiconductor device and a method of manufacturing the semiconductordevice capable of preventing solder shrinkage and minimizing a decreasein withstand voltage even when solder leakage takes place.

Measures for Solving the Problem

An embodiment according to the present invention provides asemiconductor device including a semiconductor chip, a conductive memberfor supporting the semiconductor chip, a joint material provided betweenthe conductive member and the semiconductor chip, and a release grooveformed on the surface of the conductive member and arranged away fromthe semiconductor chip with the one end and the other end thereofconnected to the peripheral edges of the conductive member,respectively.

The semiconductor device can be manufactured by an embodiment of themanufacturing method according to the present invention, which includesa step of preparing a conductive member having a release groove formedon the surface the conductive member, the release groove forming aprescribed chip area with the one end and the other end of the releasegroove connected to the peripheral edges of the conductive member, astep of placing a joint material in the chip area, a step of placing asemiconductor chip on the joint material, and a step of bonding thesemiconductor chip onto the conductive member by melting the jointmaterial while applying a load to the semiconductor chip, wherein anarea ratio of the semiconductor chip to the joint material (chiparea/joint material area) is 1.0 or less.

According to this method, solder shrinkage can be prevented regardlessof the size of a load applied to a semiconductor chip even in aconfiguration where chip area/joint material area is 1.0 or less. Sincethe area of the joint material is relatively large compared to the areaof the semiconductor chip, solder leakage is likely to occur. However,even if solder begins to leak, the leaked solder may be introduced intoa release groove. In this way, the solder can be prevented from gettingon the surface of a semiconductor chip, and thus a decrease in withstandvoltage can be minimized.

The release groove is formed with the one end and the other end thereofconnected to the peripheral edges of the conductive member,respectively. That is, the one end and the other end of the releasegroove are opened at the peripheral edges of the conductive member. Assuch, for example, when forming a release groove by press working on theconductive member, surplus conductive materials pushed out can bereleased toward an opening end of the release groove. Thereby, theconductive materials pushed out can be prevented from remaining as aprotrusion nearby the release groove, and thus a process of removing theprotrusion after press working is not required. As a result, an increasein cost required for forming a release groove can be suppressed to arelatively low level.

Further, in an embodiment of the manufacturing method according to thepresent invention, an area ratio of the semiconductor chip to the jointmaterial (chip area/joint material area) is preferably adjusted between0.6 and 0.8, inclusive. In an embodiment according to the presentinvention, it does not matter whether or not a portion of the jointmaterial gets into the release groove.

In an embodiment according to the present invention, a plurality of therelease grooves may be formed on the surface of the conductive member,and the semiconductor chips may be arranged in chip areas sandwichedbetween the plurality of release grooves.

With this configuration, whether the joint material leaks rightward orleftward in the semiconductor chip, a release groove is definitelyformed nearby the leak position, and thus a solder can be securelyprevented from getting on the surface of the semiconductor chip.

In an embodiment according to the present invention, the plurality ofthe release grooves may be formed in a stripe shape parallel to eachother.

An embodiment according to the present invention may further include astepped structure formed on the lateral surface of the release groove.

With this configuration, the joint material that gets into the releasegroove can be prevented from flowing back. Thus, the reliability ofwithstand voltage in the semiconductor device can be improved.

In an embodiment according to the present invention, the steppedstructure is configured such that the release groove is partitioned intoa plurality of stages in the depth direction, which may be formed fromthe one end to the other end of the release groove.

In an embodiment according to the present invention, the conductivemember has end surfaces that form the peripheral edges, and the one endand the other end of the release groove may be opened at the endsurfaces, respectively.

In an embodiment according to the present invention, the surface of theconductive member is formed in a rectangular shape, and the releasegroove may be formed along a pair of short sides of the rectangularlyshaped conductive member.

With this configuration, the machining dimension of the conductivemember for forming the release groove can be shorten compared to a casewhere the release groove is formed along a pair of long sides. As aresult, an increase in cost associated with the formation of the releasegroove can be further suppressed.

An embodiment according to the present invention may further include asecond conductive member arranged above the semiconductor chip, facingthe conductive member spaced apart therefrom, and a resin package thatseals the semiconductor chip, the conductive member and the secondconductive member so as to get into a space between the conductivemember and the second conductive member.

With this configuration, a portion of the resin package is sandwichedbetween the conductive member and the second conductive member to thusallow the portion to be held therebetween. Therefore, the adhesion ofthe resin package to the semiconductor chip, the conductive member andthe second conductive member can be improved.

In an embodiment according to the present invention, the conductivemember may have a rear surface exposed from the resin package to serveas a heat sink.

An embodiment according to the present invention may be a powersemiconductor module including a high-side assembly, which includes ahigh-side base member as the conductive member and a high-side switchingelement as the semiconductor chip arranged on the high-side base member;a low-side assembly, which is arranged away from the high-side assemblyand includes a low-side base member as the conductive member and alow-side switching element as the semiconductor chip arranged on thelow-side base member; and a resin package for sealing the high-sideassembly and the low-side assembly.

In an embodiment according to the present invention, each high-side basemember and low-side base member has a rear surface exposed from theresin package, which may serve as a heat sink.

An embodiment according to the present invention may include a high-sideterminal integrally formed with the high-side base member so as toproject from the resin package, and a low-side terminal arranged abovethe low-side switching element so as to project from the resin package,facing the low-side base member spaced apart therefrom.

An embodiment according to the present invention may further include arelay member arranged above the high-side switching member, electricallyconnected to the low-side base member.

An embodiment of the manufacturing method according to the presentinvention further includes a step of placing a jig with an openinghaving a planar area smaller than that of the semiconductor chip suchthat the circumferential edge of the opening comes in contact with thecircumferential edge of the semiconductor chip; a step of placing asecond joint material on the upper surface of the semiconductor chipexposed through the opening; and a step of arranging a conductive blockon the second joint material, and the bonding step may include a step ofapplying a load to the circumferential edge of the semiconductor chipusing the jig.

According to this method, a load may be evenly applied to thesemiconductor chip, and thus the joint material can be prevented frombeginning to leak biased in a specific direction. Thereby, when thejoint material begins to leak, the amount of leaked joint material canbe dispersed along the circumferential edge of the semiconductor chip,and thus the solder can be further favorably prevented from getting onthe surface of the semiconductor chip.

In an embodiment according to the present invention, the jig may have aguide portion formed by selectively elevating a part of the rear surfacethereof from a contact surface in contact with the semiconductor chip,the guide portion surrounding the semiconductor chip.

According to this method, even if a large amount of joint materialleaks, the joint material can be securely introduced to a release grooveby the guide portion of a jig.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a power semiconductor moduleillustrating an embodiment according to the present invention.

FIG. 2 is a cross-sectional view that appears when cutting the powersemiconductor module shown in FIG. 1 along a cutting line II-II.

FIG. 3 is a cross-sectional view that appears when cutting the powersemiconductor module shown in FIG. 1 along a cutting line III-III.

FIG. 4a cross-sectional view that appears when cutting the powersemiconductor module shown in FIG. 1 along a cutting line IV-IV.

FIG. 5 is an enlarged view of a region surrounded by a dashed line Vshown in FIG. 3.

FIG. 6 is a line graph illustrating a relationship between a loadapplied to a semiconductor chip and an amount of leaked solder.

FIG. 7 is a line graph illustrating a relationship between a loadapplied to a semiconductor chip and an amount of shrunk solder.

FIG. 8 is a contour graph illustrating the distribution of an amount ofleaked solder when a load applied to a semiconductor chip and chiparea/solder area are varied.

FIG. 9 is a contour graph illustrating the distribution of an amount ofshrunk solder when a load applied to a semiconductor chip and chiparea/solder area are varied.

FIG. 10A and FIG. 10B are views illustrating a part of manufacturingsteps of the power semiconductor module shown in FIG. 1. FIG. 10A is aplan view and FIG. 10B is a cross-sectional view.

FIG. 11A and FIG. 11B are views illustrating the next steps of FIG. 10Aand FIG. 10B. FIG. 11A is a plan view and FIG. 11B is a cross-sectionalview.

FIG. 12A and FIG. 12B are views illustrating the next steps of FIG. 11Aand FIG. 11B. FIG. 12A is a plan view and FIG. 12B is a cross-sectionalview.

FIG. 13A and FIG. 13B are views illustrating the next steps of FIG. 12Aand FIG. 12B. FIG. 13A is a plan view and FIG. 13B is a cross-sectionalview.

FIG. 14A and FIG. 14B are views illustrating the next steps of FIG. 13Aand FIG. 13B. FIG. 14A is a plan view and FIG. 14B is a cross-sectionalview.

EMBODIMENT FOR PRACTICING THE INVENTION

Hereinafter, an embodiment according to the present invention will bespecifically discussed with reference to the accompanying drawings.

Configuration of a Module According to an Embodiment of the PresentInvention

FIG. 1 is a schematic plan view of a power semiconductor module 1illustrating an embodiment according to the present invention. FIG. 2 isa cross-sectional view that appears when cutting the power semiconductormodule 1 shown in FIG. 1 along a cutting line II-II. FIG. 3 is across-sectional view that appears when cutting the power semiconductormodule 1 shown in FIG. 1 along a cutting line III-III. FIG. 4 is across-sectional view that appears when cutting the power semiconductormodule 1 shown in FIG. 1 along a cutting line IV-IV. FIG. 5 is anenlarged view of a region surrounded by a dashed line V shown in FIG. 3.

The power semiconductor module 1 includes a high-side assembly 2, alow-side assembly 3, a relay terminal 4 as an example of a secondconductive member and a relay member according to the present invention,and a resin package 5. The high-side assembly 2 and the low-sideassembly 3 are arranged adjacently to each other with a gap 62therebetween as shown in FIG. 1 and FIG. 2.

The high-side assembly 2 includes a high-side heat dissipation block 6as an example of the conductive member and the high-side base memberaccording to the present invention, a high-side IGBT 7 (Insulated GateBipolar Transistor (IGBT)) and a high-side FRD 8 (Fast Recovery Diode(FRD)) as examples of the semiconductor chip and the high-side switchingelement according to the present invention, a high-side contact block 9,a high-side emitter terminal 10, and a high-side gate terminal 11.Hereinafter, the high-side IGBT 7 and the high-side FRD 8 may be simplyreferred to as a chip 7 and a chip 8 (the same is true for thelater-described low-side IGBT 30 and low-side FRD 31).

The high-side heat dissipation block 6 is composed of, for example,copper (Cu). In this embodiment, the high-side heat dissipation block 6is formed in a slightly-flat rectangular parallelepiped shape(rectangular shape in plan view).

A plurality of release grooves 13 is formed on the surface 12 of thehigh-side heat dissipation block 6. Here, the release grooves 13 areshallowly formed in a region near the surface 12 (surface part) of thehigh-side heat dissipation block 6. In other words, a metal part isthickly remained below the relatively shallow release grooves 13 in thehigh-side heat dissipation block 6. This structure may prevent thehigh-side heat dissipation block 6 from being bent along the releasegrooves 13 due to heat, stress and so forth. For example, when thehigh-side heat dissipation block 6 has a thickness of 1 mm to 20 mm, therelease grooves 13 may have a depth of approximately 0.01 mm to 2 mm.

In this embodiment, each release groove 13 is formed along a pair ofshort sides of the high-side heat dissipation block 6 so as to connectboth the end surfaces 14 of a pair of long sides of the high-side heatdissipation block 6 as shown in FIG. 1. Thereby, the one end and theother end of each release groove 13 are opened at the end surfaces 14 ofthe high-side heat dissipation block 6, respectively.

Further, a stepped structure 15 is formed on the lateral surface of eachrelease groove 13. In this embodiment, the stepped structure 15 isconfigured such that the release groove 13 is partitioned into twostages in the depth direction as shown in FIG. 5. Thereby, the steppedstructure 15 includes a first groove 16 and a second groove 17 formed bythe bottom of the first groove 16 further dented, having a widthnarrower than that of the first groove 16. The stepped structure 15 iscontinuously formed along the longitudinal direction of the releasegroove 13 from the one side end surface 14 to the other side end surface14 of the high-side heat dissipation block 6 as shown in FIG. 1.

The number of stages of the stepped structure 15 is not limited to two,but may be three, four or more. Further, a plurality of grooves (firstgroove 16 and second groove 17 in this embodiment) may have mutually thesame depth or mutually different depths. The stepped structure 15 may beselectively formed along the longitudinal direction of the releasegroove 13. For example, a plurality of the second grooves 17 may beformed spaced apart from each other along the longitudinal direction ofthe release groove 13. Furthermore, the stepped structure 15 does notneed to be formed.

With such release grooves 13 formed spaced apart from each other alongthe long side of the high-side heat dissipation block 6, the surface 12of the high-side heat dissipation block 6 is divided into a plurality ofregions. In this embodiment, four release grooves 13 are formed parallelto each other as shown in FIG. 1. Thereby, three chip areas 18 areformed in a rectangular shape in plan view sandwiched between adjacentrelease grooves 13 on the surface 12 of the high-side heat dissipationblock 6.

Each one of the high-side IGBT 7 and the high-side FRD 8 is arranged ineach chip area 18. Specifically, the high-side IGBT 7 and the high-sideFRD 8 are arranged with a distance therebetween along the release groove13 in this order away from the low-side assembly 3. A prescribed gap isformed between the release groove 13, and the high-side GBT 7 and thehigh-side FRD 8.

The high-side IGBT 7 has an emitter pad 19 and a gate pad 20 on theupper surface, and has a collector pad 21 on the rear surface. Whereas,the high-side FRD 8 has an anode pad 22 on the upper surface, and has acathode pad (not shown) on the rear surface. The rear surfaces of thehigh-side IGBT 7 and the high-side FRD 8 are bonded onto the high-sideheat dissipation block 6 using a solder material 23 as an example of thejoint material according to the present invention. Thereby, thecollector of the high-side IGBT 7 and the cathode of the high-side FRD 8are electrically connected to the high-side heat dissipation block 6,respectively. For the sake of clarity, the emitter pad 19, the gate pad20, and the collector pad 21 are not shown in FIG. 2 and FIG. 3.

The solder material 23 is provided between the high-side heatdissipation block 6, and the high-side IGBT 7 and the high-side FRD 8.Further, the solder material 23 may have a leaked portion 26 leakedoutside the circumferential edge of the high-side IGBT 7 and thehigh-side FRD 8. The leaked portion 26 may get in the release groove 13,for example, as shown by a dashed line in FIG. 5.

Further, a positive (P) terminal 25 as an example of the high-sideterminal of the present invention is integrally connected to thehigh-side heat dissipation block 6. The P terminal 25 is connected to apositive side of a circuit power supply. A power supply voltage suppliedfrom the p terminal 25 is applied to the collector of the high-side IGBT7 and the cathode of the high-side FRD 8 via the high-side heatdissipation block 6. In this embodiment, as shown in FIG. 3, the Pterminal 25 projects from the end surface 24 of the short side of thehigh-side heat dissipation block 6 with the same thickness as that ofthe high-side heat dissipation block 6, extending from the inside to theoutside of the resin package 5. That is, the P terminal 25 is connectedto the end surface 24 different from the end surface 14 at which therelease groove 13 of the high-side heat dissipation block 6 is opened. Athrough-hole 54 is formed in the exposed portion of the P terminal 25.

The high-side contact block 9 is composed of, for example, copper (Cu).Each high-side contact block 9 is arranged on the emitter pad 19 of thehigh-side IGBT 7 and on the anode pad 22 of the high-side FRD 8 usingthe solder material 27. Thereby, the high-side contact block 9 iselectrically connected to the emitter pad 19 of the high-side IGBT 7 andthe anode pad 22 of the high-side FRD 8.

The high-side emitter terminal 10 and the high-side gate terminal 11 arearranged at the opposite side of the low-side assembly 3 across thehigh-side heat dissipation block 6, extending from the inside to theoutside of the resin package 5. The high-side emitter terminal 10 andthe high-side gate terminal 11 are electrically connected to the emitterpad 19 and the gate pad 20 using a bonding wire 28, respectively.

The low-side assembly 3 includes a low-side heat dissipation block 29 asan example of the conductive member and the low-side base memberaccording to the present invention, a low-side IGBT 30 and a low-sideFRD 31 as examples of the semiconductor chip and the low-side switchingelement according to the present invention, a low-side contact block 32,a low-side emitter terminal 33, a low-side gate terminal 34, and anegative (N) terminal 50 as an example of a low-side terminal accordingto the present invention.

The low-side heat dissipation block 29 is composed of, for example,copper (Cu). In this embodiment, the low-side heat dissipation block 29is formed in a slightly-flat rectangular parallelepiped shape(rectangular shape in plan view) similarly to the high-side heatdissipation block 6. The high-side heat dissipation block 6 and thelow-side heat dissipation block 29 are adjacently arranged with the endsurfaces 14, 37 of the long sides thereof facing each other.

A plurality of release grooves 36 is formed on the surface 35 of thelow-side heat dissipation block 29. Here, the release grooves 36 areshallowly formed in a region near the surface 35 (surface part) of thelow-side heat dissipation block 29. In other words, a metal part isthickly remained below the relatively shallow release grooves 36 in thelow-side heat dissipation block 29. This structure may prevent thelow-side heat dissipation block 29 from being bent along the releasegrooves 36 due to heat, stress and so forth. For example, when thelow-side heat dissipation block 29 has a thickness of 1 mm to 20 mm, therelease grooves 36 may have a depth of approximately 0.01 mm to 2 mm.

In this embodiment, each release groove 36 is formed along a pair ofshort sides of the low-side heat dissipation block 29 so as to connectboth the end surfaces 37 of a pair of long sides of the low-side heatdissipation block 29 as shown in FIG. 1. Thereby, the one end and theother end of each release groove 36 are opened at the end surfaces 37 ofthe low-side heat dissipation block 29, respectively.

Further, a stepped structure 38 is formed on the lateral surface of eachrelease groove 36. In this embodiment, the stepped structure 38 isconfigured such that the release groove 36 is partitioned into twostages in the depth direction similarly to the stepped structure 15 asshown in FIG. 5. That is, the stepped structure 38 includes a firstgroove and a second groove (not shown) having the same structures asthose of the first groove 16 and the second groove 17 shown in FIG. 5.The stepped structure 38 is continuously formed along the longitudinaldirection of the release groove 36 from the one side end surface 37 tothe other side end surface 37 of the low-side heat dissipation block 29as shown in FIG. 1.

With such release grooves 36 formed spaced apart from each other alongthe long side of the low-side heat dissipation block 29, the surface 35of the low-side heat dissipation block 29 is divided into a plurality ofregions. In this embodiment, four release grooves 36 are formed parallelto each other. Thereby, three chip areas 41 are formed in a rectangularshape in plan view sandwiched between adjacent release grooves 36 on thesurface 35 of the low-side heat dissipation block 29. The releasegrooves 36 may be formed along the longitudinal direction of the releasegroove 13 of the high-side heat dissipation block 6 as shown in FIG. 1or may be formed along a direction orthogonal to the longitudinaldirection of the release groove 13.

Each one of the low-side IGBT 30 and the low-side FRD 31 is arranged ineach chip area 41. Specifically, the low-side IGBT 30 and the low-sideFRD 31 are arranged with a distance therebetween along the releasegroove 36 in this order away from the high-side assembly 2. A prescribedgap is formed between the release groove 36, and the low-side GBT 30 andthe low-side FRD 31.

The low-side IGBT 30 has an emitter pad 42 and a gate pad 43 on theupper surface, and has a collector pad (not shown) on the rear surface.Whereas, the low-side FRD 31 has an anode pad 44 on the upper surface,and has a cathode pad (not shown) on the rear surface. The rear surfacesof the low-side IGBT 30 and the low-side FRD 31 are bonded onto thelow-side heat dissipation block 29 using a solder material 45 as anexample of the joint material according to the present invention.Thereby, the collector of the low-side IGBT 30 and the cathode of thelow-side FRD 31 are electrically connected to the low-side heatdissipation block 29, respectively.

The solder material 45 is provided between the low-side heat dissipationblock 29, and the low-side IGBT 30 and the low-side FRD 31. Further, thesolder material 45 may have a leaked portion 37 leaked outside thecircumferential edge of the low-side IGBT 30 and the low-side FRD 31similarly to the solder material 23. The leaked portion 39 may get inthe release groove 36 similarly to the leaked portion 26 as shown inFIG. 5.

Further, an output terminal 46 is integrally connected to the low-sideheat dissipation block 29. The output terminal 46 is connected to theload of a circuit. In this embodiment, the output terminal 46 projectsfrom the end surface 47 of the short side of the low-side heatdissipation block 29 with the same thickness as that of the low-sideheat dissipation block 29, extending from the inside to the outside ofthe resin package 5 as shown in FIG. 4. That is, the output terminal 46is connected to the end surface 47 different from the end surface 37 atwhich the release groove 36 of the low-side heat dissipation block 29 isopened. Further, in this embodiment, the end surface 47 to which theoutput terminal 46 is connected is the end surface 47 on the oppositeside of the end surface 47 adjacent to the P terminal 25. Thereby, theoutput terminal 46 extends in a direction opposite to the P terminal 25.A through-hole 55 is formed in the exposed portion of the outputterminal 46.

The low-side contact block 32 is composed of, for example, copper (Cu).Each low-side contact block 32 is arranged on the emitter pad 42 of thelow-side IGBT 30 and the anode pad 44 of the low-side FRD 31 using thesolder material 45. Thereby, the low-side contact block 32 iselectrically connected to the emitter pad 42 of the low-side IGBT 30 andthe anode pad 44 of the low-side FRD 31.

The low-side emitter terminal 33 and the low-side gate terminal 34 arearranged at the opposite side of the high-side assembly 2 across thelow-side heat dissipation block 29, extending from the inside to theoutside of the resin package 5. The low-side emitter terminal 33 and thelow-side gate terminal 34 are electrically connected to the emitter pad42 and the gate pad 43 using a bonding wire 49, respectively.

An N terminal 50 is composed of, for example, copper (CU), and is formedin a block shape with the same thickness as that of the high-side heatdissipation block 6 and the low-side heat dissipation block 29. The Nterminal 50 is connected to all the low-side contact blocks 32 on thelow-side IGBT 30 and the low-side FRD 31 using the solder material 51.

Specifically, the N terminal 50 extends along the long side of thelow-side heat dissipation block 29 to traverse a plurality of chip areas41 in plan view. The longitudinal placement area of the N terminal 50,for example, extends from one end surface 47 of the low-side heatdissipation block 29 to the outside of the resin package 5. Thereby, theN terminal 50 projects from the resin package 5 while forming a space 52with the low-side heat dissipation block 29 inside the resin package 5.A through-hole 56 is formed in the exposed portion of the N terminal 50.In this embodiment, the projection direction of the N terminal 50 is thesame as the projection direction of the P terminal 25, that is, theprojection direction of the N terminal 50 is opposite to the projectiondirection of the output terminal 46 included in the same low-sideassembly 3. Thereby, the N terminal 50 and the output terminal 46 do notoverlap each other, and thus do not interfere with each other.

Meanwhile, the N terminal 50 is formed narrower in width than thelow-side heat dissipation block 29. The difference in the widthdirection between the N terminal 50 and the low-side heat dissipationblock 29 allows a contact area 53 to be formed on the low-side heatdissipation block 29, the contact area laterally extending from the Nterminal 50 and forming a part of the chip area 41.

The N terminal 50 is connected to the negative side of a power supplycircuit. The power supply voltage supplied from the N terminal 50 isapplied to the emitter of the low-side IGBT 30 and the anode of thelow-side FRD31 via the low-side contact block 32.

The relay terminal 4 is composed of, for example, copper (Cu) and isformed with the same thickness as the high-side heat dissipation block 6and the low-side heat dissipation block 29. The relay terminal 4 isarranged above the high-side heat dissipation block 6 and the low-sideheat dissipation block 29 extending across both components. Thereby, therelay terminal 4 forms a space 57 with the high-side heat dissipationblock 6 and the low-side heat dissipation block 29. Specifically, therelay terminal 4 extends along the long side of the high-side heatdissipation block 6 and the low-side heat dissipation block 29,traversing a plurality of chip areas 18, 41 in plan view. Thelongitudinal placement area of the relay terminal 4, for example,extends from the one end surface 24, 47 to the other end surface 24, 47of each heat dissipation block 6, 29.

The relay terminal 4 is bonded onto all the high-side contact blocks 9on the high-side IGBT 7 and the high-side FRD 8 in the high-sideassembly 2 using the solder material 58. Meanwhile, the relay terminal 4is bonded onto the low-side heat dissipation block 29 in the low-sideassembly 3 using the relay block 59.

Each relay block 59 is arranged in each contact area 53 of the low-sideheat dissipation block 29 via a solder material 60. Each solder material61 is provided between each relay block 59 and the relay terminal 4.

As shown in FIG. 2, a current flows from the emitter of the high-sideIGBT 7 and the anode of the high-side FRD 8 to the collector of thelow-side IGBT 30 and the cathode of the low-side FRD 31 through therelay terminal 4, the relay block 59, and the low-side heat dissipationblock 29.

The resin package 5 is, for example, an epoxy resin. The resin package 5covers the high-side assembly 2, the low-side assembly 3, the relayterminal 4 and so forth so as to expose each rear surface 63, 64 of thehigh-side heat dissipation block 6 and the low-side heat dissipationblock 29. The heat generated in each chip 7, 8, 30, 31 is diffused fromthe rear surfaces 63, 64 of the high-side heat dissipation block 6 andthe low-side heat dissipation block 29. Further, in this embodiment, apart of the resin package 5 gets into the space 52, 57. Thereby, thepart of the resin package 5 is sandwiched and held between the lowerside conductive member (high-side heat dissipation block 6 and low-sideheat dissipation block 29) and the upper side conductive member (relayterminal 4 and N terminal 50). As a result, the adhesion of the resinpackage 5 to the high-side assembly 2, low-side assembly 3, the relayterminal 4 and so forth can be improved.

<Pre-Evaluation to Come Up with the Present Invention>

The inventors of the present invention have evaluated the relationshipbetween an amount of leaked solder (an amount of shrunk solder) and aload applied to a semiconductor chip (IGBT) by experiment to determinethe cause of solder leakage and solder shrinkage in the bonding of asemiconductor chip. The results are shown in FIGS. 6-9. FIGS. 6-7 areline graphs representing the relationship between a load applied to asemiconductor chip and an amount of leaked solder (an amount of shrunksolder). Here, an amount of leaked solder (an amount of shrunk solder)with respect to a semiconductor chip is considered, but thelater-described release groove is not taken into account. FIG. 8 andFIG. 9 are a contour graph illustrating the distribution of an amount ofleaked solder (an amount of shrunk solder) when a load applied to asemiconductor chip and chip area/solder area are varied. A contour lineis input within the range of experiment. In FIG. 8 and FIG. 9, thenumerical values put on each lead line represent the amounts of leakedsolder (mm³) and the amounts of shrunk solder (mm²) in the regionsindicated by the lead lines.

According to FIGS. 6-9, it was found that the smaller the load is, themore effectively the solder leakage can be suppressed regardless of thesize of the chip area/solder area. Although conventionally it wasthought that the shortage of a load applied to a semiconductor chip andthe shortage of an amount of solder could cause solder shrinkage, it wasfound that solder shrinkage cannot be completely controlled only by anapplied load and an amount of solder. For example, according to the data(IGBT) shown in FIG. 7, the solder shrinkage increases fromapproximately 1.6 mm² to approximately 2.2 mm² despite an increase inapplied load from 40 g to 160 g. That is, although conventionally it wasthought that there is a conflicting relation between solder leakage andsolder shrinkage, it was found that the conflicting relation is notnecessarily applicable in every case according to FIG. 6 to FIG. 9.

Here, the inventors of this application are motivated to form therelease grooves 13, 36 with both ends opened in the high-side heatdissipation block 6 and the low-side heat dissipation block 29 aspreviously described, while setting the value of chip area/solder areain manufacturing steps within a suitable range. Thereby, it was foundthat a semiconductor device can be provided, which is capable ofpreventing solder shrinkage while minimizing a decrease in withstandvoltage at low cost.

<Steps of Manufacturing a Module According to an Embodiment of thePresent Invention>

Hereinafter, as a result of reviewing FIGS. 6-9, the specific aspect ofthe bonding of semiconductor chips in the steps of manufacturing asemiconductor device will be discussed by taking the above-describedhigh-side assembly 2 as an example.

FIG. 10A, FIGS. 10B-14A, and FIG. 14B are views illustrating a part ofmanufacturing steps of the power semiconductor module 1 shown in FIG. 1in order of steps (manufacturing steps of high-side assembly 2). FIG.10A is a plan view corresponding to FIG. 1, and FIG. 10B is across-sectional view corresponding to FIG. 5. Some reference numeralsshown in FIG. 1 and FIG. 5 are omitted in FIG. 10A, FIGS. 10B-14A, andFIG. 14B for the sake of clarity.

When manufacturing the high-side assembly 2, first, the high-side heatdissipation block 6 with a release groove 13 formed thereon is preparedas shown in FIG. 10A and FIG. 10B. The release groove 13 may be formedon the surface 12 of the high-side heat dissipation block 6, forexample, by press working after the high-side heat dissipation block 6is molded.

Next, as shown in FIG. 11A and FIG. 11B, plate shaped solder 65 as anexample of the joint material according to the present invention isplaced at a prescribed position in the chip area 18. The size of theplate shaped solder 65 is adjusted such that the ratio of the areas ofthe high-side GBT 7 and the high-side FRD 8 to the solder area (chiparea/solder area) is 1 or less. In this embodiment, the plate shapedsolder 65 that is smaller in size than each chip 7, 8 is used within theabove described range. Solder paste may be used in place of the plateshaped solder 65.

Next, the high-side IGBT 7 and the high-side FRD 8 are placed on eachplate shaped solder 65, respectively as shown in FIG. 12A and FIG. 12B.

Next, as shown in FIG. 13A and FIG. 13B, a jig 66 is set to apply a loadto the high-side heat dissipation block 6.

The jig 66 has a plurality of openings 67 in accordance with thearrangement pattern of the high-side IGBT 7 and the high-side FRD 8.Each opening has an area smaller than the areas of the high-side IGBT 7and the high-side FRD 8. Further, the jig 66 has a guide portion 69selectively elevated from a circumferential edge 68 of the opening 67 ata portion facing the release groove 13. The guide portion 69 may beformed in a stripe shape as in the release groove 13, or may beselectively formed in the periphery of the opening 67.

The jig 66 is placed to allow the circumferential edge 68 of the opening67 to come in contact with the circumferential edge of each chip 7, 8with each opening 67 aligned with each chip 7, 8. In this state, plateshaped solder 70 as an example of a second joint material according tothe present invention and a high-side contact block 9 as an example ofthe conductive block according to the present invention are furtherplaced on each chip 7, 8 exposed through the opening 67.

Next, as shown in FIG. 14A and FIG. 14B, the high-side contact block 9and the jig 66 are heated while a load is applied thereto. Thereby, themolten plate shaped solder 65 is pressed and crushed by each chip 7, 8,and spreads to form the solder material 23. Also, the plate shapedsolder 70 is melted to form the solder material 27. At this time, thecircumferential edge of each chip 7, 8 is pressed by the circumferentialedge 68 of the opening of the jig 66, and thus a load may be evenlyapplied to the chips 7, 8. As a result, molten solder can be preventedfrom leaking biased in a specific direction. Thus, the leaked mount ofsolder 23 can be dispersed along the circumferential edge of the chips7, 8. The high-side assembly 2 can be obtained by following the stepsdescribed above.

The power semiconductor module 1 can be manufactured by obtaining thelow-side assembly 3 in the same manner as the high-side assembly 2,connecting both assemblies 2, 3 with the relay terminal 4, thereaftersealing these assemblies with the resin package 5.

According to the manufacturing method described above, in the bonding ofthe high-side IGBT 7 and the high-side FRD 8, the area ratio of thechips 7, 8 to the plate shaped solder 65 (chip area/solder area) is setto 1 or less. Thereby, solder shrinkage can be suppressed regardless ofthe size of a load applied to the high-side IGBT 7 and the high-side FRD8. Particularly, solder shrinkage can be prevented by reducing the arearatio to 0.8 or less and increasing the amount of solder.

Meanwhile, since the area of the plate shaped solder 65 is relativelylarge compared to the area of the chips 7, 8, solder leakage from thechips 7, 8 may occur as shown in FIG. 14. However, even if solder beginsto leak, the solder may be introduced to the release groove 13.Particularly, in this embodiment, the release groove 13 is formed onboth sides of each chip area 18 while the guide portion 69 is formed inthe jig 66. As such, the solder that begins to leak can be introduced inthe release groove 13. That is, when the solder leakage to the outsideof area including the release groove 13 (outside solder leakage) isassumed here, the outside solder leakage can be reduced to zero with thearea ratio set no greater than 1. As a result, a portion of the soldermaterial 23 can be prevented from getting on the surface of the chips 7,8, and thus a decrease in withstand voltage can be minimized. Meanwhile,if the area ratio is less than 0.6, surplus solder overflows from theopen end of the release groove 13, and therefore the area ratio ispreferably 0.6 or greater.

The one end and the other end of each release groove 13 are respectivelyopened at the end surfaces 14 of the high-side heat dissipation block 6.Therefore, for example, when the release groove 13 is formed by presswording on the high-side heat dissipation block 6, the surplus coppermaterial pushed out can be released toward the open end of the releasegroove 13. Thereby, the copper material pushed out can be suppressedfrom remaining as a protrusion in the periphery of the release groove13, and thus machining work after press working for removing theprotrusion is not required. As a result, an increase in cost necessaryfor forming the release groove 13 can be reduced to a relatively lowlevel. Further, in this embodiment, the release groove 13 is formedalong the short side of the high-side heat dissipation block 6.Accordingly, the machining dimension of the high-side heat dissipationblock 6 for forming the release groove 13 can be shorten compared to acase where the release groove 13 is formed along the long side. As aresult, an increase in cost associated with the formation of the releasegroove 13 can be further minimized.

Once solder gets into the release groove 13, the solder can beintroduced by its own weight to the second groove 17 located at arelatively deep position. Thus, provided that the amount of leakedsolder has approximately the same volume as that of the second groove17, the whole amount of leaked solder can be stored in the deepest area(second groove 17) in the release groove 13. Thereby, the solder in therelease groove 13 is prevented from flowing back, and thus thereliability of withstand voltage can be improved.

An embodiment according to the present invention has been described asabove, however, the present invention may be practiced also in otherembodiments.

For example, in the previously described embodiment, an example is shownin which the release grooves 13, 36 are formed in the high-side heatdissipation block 6 and the low-side heat dissipation block 29, whichare used as a heat sink. However, the structure such as the releasegrooves 13, 36 can also be formed, for example, in the island of a leadframe.

Further, the high-side heat dissipation block 6 and the low-side heatdissipation block 29 do not need to be formed in a rectangular shape inplan view. For example, these blocks may be formed in other polygonalshapes (for example, triangular shape, pentagonal shape) or in acircular shape.

Further, the release grooves 13, 36 do not need to be formed in a stripeshape, but may be formed, for example in a meander pattern.

Further, the present invention may be applied to other module products,discrete products and so forth, not limited to a power semiconductormodule.

It is to be understood that variations and modifications can be madewithout departing from the scope and spirit of the present invention.

This application corresponds to Patent Application No. 2014-041862submitted to Japanese Patent Office on Mar. 4, 2014, and the entirecontents of this application are hereby incorporated by reference.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1 Power semiconductor module-   2 High-side assembly-   3 Row-side assembly-   4 Relay terminal-   5 Resin package-   6 High-side heat dissipation block-   7 High-side IGBT-   8 High-side FRD-   9 High-side contact block-   12 (High-side heat dissipation block) surface-   13 Release groove-   14 (Long side of high-side heat dissipation block) end surface-   15 Stepped structure-   16 First groove-   17 Second groove-   18 Chip area-   23 Solder material-   24 (Short side of high-side heat dissipation block) end surface-   25 P terminal-   26 Leaked portion-   27 Solder material-   29 Low-side heat dissipation block-   30 Low-side IGBT-   31 Low-side FRD-   32 Low-side contact block-   35 (Low-side heat dissipation block) surface-   36 Release groove-   37 (Long side of low-side heat dissipation block) end surface-   38 Stepped structure-   39 Leaked portion-   41 Chip area-   45 Solder material-   46 Output terminal-   47 (Short side of low-side heat dissipation block) end surface-   50 N terminal-   51 Solder material-   52 Space-   53 Contact area-   57 Space-   59 Relay block-   63 (High-side heat dissipation block) rear surface-   64 (Low-side heat dissipation block) rear surface-   65 Plate shaped solder-   66 Jig-   67 (Jig) opening-   68 (Jig opening) circumferential edge-   69 Guide portion-   70 Plate shaped solder

What is claimed is:
 1. A semiconductor device comprising: asemiconductor chip; a conductive member for supporting the semiconductorchip; a joint material provided between the conductive member and thesemiconductor chip; a release groove formed on a surface of theconductive member and arranged away from the semiconductor chip with afirst end and a second end of the release groove connected to peripheraledges of the conductive member, respectively; a second conductive memberarranged above the semiconductor chip, facing the conductive memberspaced apart therefrom; and a resin package that seals the semiconductorchip, the conductive member, and the second conductive member such thata part of the resin package is located in a space between the conductivemember and the second conductive member.
 2. A semiconductor deviceaccording to claim 1, wherein a plurality of the release grooves isformed on the surface of the conductive member, and the semiconductorchip is arranged in a chip area sandwiched between the plurality of therelease grooves.
 3. A semiconductor device according to claim 2, whereinthe plurality of the release grooves is formed in a stripe shapeparallel to each other.
 4. A semiconductor device according to claim 1,further comprising: a stepped structure formed on a lateral surface ofthe release groove.
 5. A semiconductor device according to claim 4,wherein the stepped structure is formed by partitioning the releasegroove into a plurality of stages in a depth direction, the steppedstructure extending from the first end to the second end of the releasegroove.
 6. A semiconductor device according to claim 1, wherein theconductive member has end surfaces forming the peripheral edges, and thefirst end and the second end of the release groove are opened at the endsurfaces, respectively.
 7. A semiconductor device according to claim 1,wherein the surface of the conductive member is formed in a rectangularshape, and the release groove is formed along a pair of short sides ofthe rectangular conductive member.
 8. A semiconductor device accordingto claim 1, wherein the conductive member has a rear surface exposedfrom the resin package to serve as a heat sink.
 9. A semiconductordevice comprising: a semiconductor chip; a conductive member forsupporting the semiconductor chip; and a joint material provided betweenthe conductive member and the semiconductor chip; a release grooveformed on a surface of the conductive member and arranged away from thesemiconductor chip with a first end and a second end of the releasegroove connected to peripheral edges of the conductive member,respectively, wherein the semiconductor device is a power semiconductormodule including: a high-side assembly, which includes a high-side basemember as the conductive member and a high-side switching element as thesemiconductor chip arranged on the high-side base member, a low-sideassembly, which is arranged away from the high-side assembly andincludes a low-side base member as the conductive member and a low-sideswitching element as the semiconductor chip arranged on the low-sidebase member, and a resin package for sealing the high-side assembly andthe low-side assembly.
 10. A semiconductor device according to claim 9,wherein the high-side base member and the low-side base member have rearsurfaces exposed from the resin package, respectively, to serve as aheat sink.
 11. A semiconductor device according to claim 9, wherein thesemiconductor device includes: a high-side terminal integrally formedwith the high-side base member so as to project from the resin package;and a low-side terminal arranged above the low-side switching element soas to project from the resin package, facing the low-side base memberspaced apart therefrom.
 12. A semiconductor device according to claim 9,further comprising: a relay member arranged above the high-sideswitching element, electrically connected to the low-side base member.13. A method for manufacturing a semiconductor device comprising: a stepof preparing a conductive member having a release groove formed on asurface thereof, the release groove forming a prescribed chip area witha first end and a second end of the release groove connected toperipheral edges of the conductive member, a step of placing a jointmaterial in the prescribed chip area; a step of placing a semiconductorchip on the joint material; a step of bonding the semiconductor chiponto the conductive member by melting the joint material while applyinga load to the semiconductor chip; a step of placing a jig with anopening having a planar area smaller than that of the semiconductor chipsuch that a circumferential edge of the opening comes in contact with acircumferential edge of the semiconductor chip; a step of placing asecond joint material on an upper surface of the semiconductor chipexposed through the opening; and a step of arranging a conductive blockon the second joint material, wherein an area ratio of the semiconductorchip to the joint material is 1.0 or less, and the step of bondingfurther comprises a step of applying a load to the circumferential edgeof the semiconductor chip using the jig.
 14. A method for manufacturinga semiconductor device according to claim 13, wherein the area ratio ofthe semiconductor chip to the joint material is 0.6-0.8.
 15. A methodfor manufacturing a semiconductor device according to claim 13, whereinthe jig has a guide portion formed by selectively elevating a part of arear surface thereof from a contact surface in contact with thesemiconductor chip, the guide portion surrounding the semiconductorchip.
 16. A semiconductor device comprising: a conductive member; aplurality of semiconductor chips arranged along a first direction on theconductive member; a joint material provided between the conductivemember and each semiconductor chip; a release groove formed on a surfaceof the conductive member and arranged away from each semiconductor chipwith a first end and a second end of the release groove connected toperipheral edges of the conductive member, respectively, and the releasegroove extending parallel to the first direction; and a conductive blockarranged on each semiconductor chip.
 17. A semiconductor deviceaccording to claim 16, further comprising: a second conductive memberspanning the plurality of semiconductor chips in the first direction andcollectively connected to the plurality of semiconductor chips.
 18. Asemiconductor device according to claim 16, wherein the conductiveblocks on the plurality of the semiconductor chips have approximatelysame heights as each other.